Low ambient cooling kit for variable refrigerant flow heat pump

ABSTRACT

Systems and methods for low ambient air temperature cooling in air-source based heat pump systems wherein an outdoor heat pump unit includes a discharge hood positionable over its fan. The hood including a damper that is openable and closeable as a function of outside temperature. The outdoor unit may also include wind deflectors positioned over the coil openings of the disclosure. During cooling operations below a low outside air threshold temperature, e.g., below 23° F., the damper assembly partially closes to reduce airflow across the condenser coil of the outdoor unit to a level below that which is possible at minimum fan speed. As the outdoor temperature continues to drop, the damper assembly continues to close to further reduce airflow.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of copending Ser.No. 12/854318 filed Aug. 11, 2010, which application is fullyincorporated hereby by reference.

FIELD

The subject matter described herein relates generally to heat pumps and,more particularly, to systems and methods that facilitate low ambienttemperature cooling in variable refrigerant flow heat pumps.

BACKGROUND

Heat pump systems used for air conditioning and heating commonly consistof indoor units combined with outdoor units to provide heating andcooling for indoor spaces. Cooling and heating is achieved through avapor compression cycle. Heat is absorbed from the indoor space (coolingthe space) through the indoor unit and discharged to the outdoors at theoutdoor unit. Heating is achieved by reversing the cycle. Heat isabsorbed from the outside at the outdoor unit and discharged to theinside through the indoor units.

For air-source based heat pumps, the cooling operation tends to becomeunstable and system capacity starts to drop off as the ambient airtemperature drops below a low ambient threshold temperature, e.g., below23° F. (−5° C.). Wind blowing against the coil surfaces, which tend tobe exposed to ambient conditions, can exacerbate the negative affect adrop in ambient air temperature below the low ambient thresholdtemperature has on system stability and capacity.

Attempts to combat the negative affects of low ambient air temperatureand wind have included installing wind guards that actually restrict theairflow to allow a lower outdoor operating temperature. In such designs,however, the restriction tends to be constant which negatively impactscapacity both when cooling at higher outdoor temperatures and during theheating mode.

It is desirable to provide systems and methods that facilitate lowambient air temperature cooling in air-source based heat pump systems.

SUMMARY

Embodiments provided herein are directed to improved systems and methodsthat facilitate low ambient air temperature cooling in air-source basedheat pump systems. In a heat pump system used for air conditioning andheating that comprises indoor units combined with an outdoor unit toprovide heating and cooling of indoor spaces, an outdoor heat pump unitpreferably includes a discharge hood positionable over the fan andattachable to the top of the enclosure about the fan to capture the fandischarge. The discharge hood preferably includes a damper that isopenable and closeable as a function of outside temperature. Inaddition, the outdoor unit preferably includes wind deflectorsattachable to the sides and the back of the enclosure and positionedover the condenser coil openings in the disclosure.

During cooling operations below a low outside air threshold temperatureof, e.g., 23° F., the outdoor unit draws air around the tops and bottomsof the wind deflectors and discharges the air out the discharge hoodthrough the damper. This air is drawn across the coil surface of theheat exchanger of the outdoor unit which is under or behind the winddeflectors. The coil surface is warmer than the outdoor air so it givesup heat to the outdoors. Since the air is below the low outside airthreshold temperature only a small condenser circuit is active and thecondenser fan is operating at its lowest speed. The condensing pressurecontinues to drop as the outdoor temperature continues to drop furtherbelow the low outside air threshold temperature. To maintain a stablecondensing pressure, the damper assembly partially closes to a positionthat is a function of the outdoor ambient temperature. By partiallyclosing the damper assembly and reducing or constricting the opening ofthe discharge outlet, airflow through the condenser coil of the outdoorunit is reduced even further than enabled by the minimum speed of thefan. As the outdoor temperature continues to drop, the damper assemblycontinues to close further reducing the airflow. If the load in theindoor space increases, more airflow across the coil is required tostill maintain a suitable condensing pressure. In this case the speed ofthe fan will increase to force more air through the partially closeddamper. For varying load conditions, the condensing pressure is tuned oradjusted by varying the speed of the fan.

In another embodiment, the discharge hood includes an integral winddeflector positionable over the coil surface on a back side of theoutside unit. The wind deflector can include a second damper assemblypositioned adjacent the height of the fan and closed when the outsidetemperature is above the low outside threshold temperature and openedwhen the outside temperature is below the low outside thresholdtemperature to allow discharge air to re-circulate over the coilsurface.

In yet another embodiment, the discharge hood and integral winddeflector includes a third damper assembly positioned toward the bottomof the wind deflector. The third damper assembly is open when theoutside temperature is above the low outside threshold temperature toenable outside air to circulate over the coil surface and claosed whenthe outside temperature is below the low outside threshold temperatureto prevent the cool outside air from circulating over the coil surface.

Other systems, methods, features and advantages of the exampleembodiments will be or will become apparent to one with skill in the artupon examination of the following figures and detailed description.

BRIEF DESCRIPTION OF FIGURES

The details of the example embodiments, including structure andoperation, may be gleaned in part by study of the accompanying figures,in which like reference numerals refer to like parts. The components inthe figures are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention. Moreover, allillustrations are intended to convey concepts, where relative sizes,shapes and other detailed attributes may be illustrated schematicallyrather than literally or precisely.

FIG. 1 is a schematic of a heat pump system used for heating and coolingindoor spaces of a building.

FIG. 2A is a schematic showing the components of a vapor compressioncycle of a heat pump system.

FIG. 2B is a schematic showing the principals of heat exchange of avapor compression cycle of a heat pump system at high ambientconditions.

FIG. 2C is a schematic showing the principals of heat exchange of avapor compression cycle of a heat pump system at low ambient conditions

FIG. 3 is a side view of an outdoor heat pump of the heat pump systemshowin in FIG. 1.

FIG. 4A is a perspective view of the outdoor heat pump sown in FIG. 3.

FIG. 4B is a perspective view of an alternative configuration of theheat pump system shown in FIG. 3.

FIG. 5 is a side view of an outdoor heat pump with a discharge hood andwind deflectors.

FIG. 6 is a perspective view of the discharge hood.

FIG. 7 is a perspective view of an alternative configuration of thedischarge hood.

FIG. 8 is a perspective view of a wind deflector.

FIG. 9 is a partial side view of a wind deflector mounted on an outdoorheat pump.

FIG. 10 is a side view of the outdoor heat pump illustrating operationof the outdoor heat pump.

FIG. 11 is a side view of the outdoor heat pump illustrating operationof the outdoor heat pump.

FIG. 12 is a side view of the outdoor heat pump illustrating operationof the outdoor heat pump.

FIG. 13 is a side view of the outdoor heat pump illustrating operationof the outdoor heat pump.

FIG. 14 is a schematic of the control box of the discharge hood.

FIGS. 15A and 15B are side views of an alternative embodiment of theoutdoor heat pump illustrating operation of the outdoor heat pump.

FIGS. 16A and 16B are side views of an alternative embodiment of theoutdoor heat pump illustrating operation of the outdoor heat pump.

FIG. 17 is a schematic showing the components of a vapor compressioncycle with various tempature and pressure sensors.

It should be noted that elements of similar structures or functions aregenerally represented by like reference numerals for illustrativepurpose throughout the figures. It should also be noted that the figuresare only intended to facilitate the description of the preferredembodiments.

DESCRIPTION

Each of the additional features and teachings disclosed below can beutilized separately or in conjunction with other features and teachingsto systems and methods that facilitate low ambient air temperaturecooling in air-source based heat pump systems. Representative examplesof the present invention, which examples utilize many of theseadditional features and teachings both separately and in combination,will now be described in further detail with reference to the attacheddrawings. This detailed description is merely intended to teach a personof skill in the art further details for practicing preferred aspects ofthe present teachings and is not intended to limit the scope of theinvention. Therefore, combinations of features and steps disclosed inthe following detail description may not be necessary to practice theinvention in the broadest sense, and are instead taught merely toparticularly describe representative examples of the present teachings.

Moreover, the various features of the representative examples and thedependent claims may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings. In addition, it is expressly noted that allfeatures disclosed in the description and/or the claims are intended tobe disclosed separately and independently from each other for thepurpose of original disclosure, as well as for the purpose ofrestricting the claimed subject matter independent of the compositionsof the features in the embodiments and/or the claims. It is alsoexpressly noted that all value ranges or indications of groups ofentities disclose every possible intermediate value or intermediateentity for the purpose of original disclosure, as well as for thepurpose of restricting the claimed subject matter.

Improved systems and methods are provided that facilitate low ambientair temperature cooling in air-source based heat pump systems. Turningto the figures, FIG. 1 shows a heat pump system 10 used for airconditioning and heating that comprises indoor units 18 and 19 combinedwith an outdoor unit 12 to provide heating and cooling for indoor spaces13 of a building 11. As shown, the outdoor unit 12 is coupled throughfluid piping 16 to a fluid manifold 14, which is in turn coupled to thevarious indoor units 18 and 19. Cooling and heating is achieved througha vapor compression cycle. Heat is absorbed from the indoor space 13(cooling the space) through the indoor units 18 and 19 and discharged tothe outdoors at the outdoor unit 12. Heating is achieved by reversingthe cycle. Heat is absorbed from the outside at the outdoor unit 12 anddischarged to the indoor space 13 through the indoor units 18 and 19.

Alternatively, the system 10 can operate as a heat recovery system whichcan take heat from indoor spaces 13 using a first set of indoor units 19for spaces requiring cooling and through the vapor compression cycle,discharge this heat to indoor spaces 13 requiring heat using a secondset of indoor units 18. This is called a simultaneous heating andcooling operation.

The components of a vapor compression cycle of a heat pump system 20 aredepicted in FIG. 2A. A working fluid, i.e., a refrigerant, in itsgaseous state, is pressurized and circulated through the system 20 by acompressor 28. Upon exiting the compressor 28, the refrigerant, which isin a hot and highly pressurized vapor state, is passed through a hightemperature heat exchanger 22, commonly referred to as a condenser. Therefrigerant is cooled in the heat exchanger 22 until it condenses into ahigh pressure, moderate temperature liquid. The condensed refrigerantthen passes through an expander 24 or pressure-lowering device such asan expansion valve, capillary tube, a turbine or other work extractingdevice. From the expander 24, the low pressure refrigerant then passesthrough another heat exchanger 26, a low temperature heat exchangercommonly referred to as an evaporator. Through heat absorption in theevaporator 26, the refrigerant evaporates into a vapor. Upon exiting theevaporator 26, the refrigerant returns to the compressor 28 to repeatthe cycle.

Refering to FIGS. 2B and 2C, the principal of operation of the vaporcompression cycle of the heat pump system 20 is defined by theexpression ΔT=T_(Refrigerant)-T_(Ambient). The larger ΔT is, the easierthe heat exchange will be. However, the compressor must work harder togain a large ΔT. For example, the heat pump system 20 might be designedto balance between power consumption at the compressor 28 and thecapacity of the condenser 22 at an outside air temperature of 95° F.with a targeting in-room temperature as the goal temperature of the heatpump system 20. If a heat pump system is designed to keep the in-roomtemperature to 77° F., the targeting in-room temperature is 77° F. Theequation above is re-written as follows:ΔT=T_(Targeting In-room Temperature)-T_(Refrigerant Evaporating Temperature).If the refrigerant evaporating temperature is 50 F, the ΔT is 27° F. Thelow outside air threshold temperature is defined as follows:T_(Low Outside Air Threshold Temperature)=T_(Refrigerant CondensingTemperature)-ΔT.Assuming the refrigerant condensing temperature is also 50° F., the lowoutside air threshold temperature is 23° F. In a low outside airtemperature environment, the compressor 20 must work hard to compressthe refrigerant even at 50° F. so that the condenser 22 can perform heatexchange between the refrigerant and the outside air with thetemperature of about 23° F.

Referring to FIGS. 3 and 4 a, the outdoor unit 12 or outdoor heat pumpof the heat pump system 10 is shown. As depicted, the outdoor unit 12includes a box-like enclosure 30 having a front 33, a back 34, sides 38and a fan 32 mounted on the top 31 of the enclosure 30 and incommunication with the interior of the enclosure 30. The fan 32preferably includes a variable speed outdoor fan motor. In oneembodiment, the outdoor unit 12 can include a raised base 39 thatextends from the bottom 37 of the enclosure 30. In another embodiment,as depicted in FIG. 4B, an outdoor unit 12′ could include two or morefans 32 and 32′.

The outdoor unit 12 further comprises an expander and a compressorcoupled to a heat exchanger (see, e.g., FIG. 2). The heat exchangerpreferably comprising multi-circuited condenser coils. The outdoor heatpump 12 is preferably a variable refrigerant flow heat pump wherein thecompressor is preferably an inverter driven, i.e., variable speed,scroll compressor. Openings 35 formed in the back 34 and sides 38 of theenclosure 30 expose the coil surfaces 36 of the heat exchanger tooutdoor ambient conditions.

During normal cooling operation, i.e., operation above approximately 23°F. outdoor ambient air temperature, the outdoor unit 12 draws airthrough the back 34 and both sides 38, and discharges air out the top 31of the enclosure 30. The air is drawn across the surface 36 of thecondenser coils, which is exposed on three sides, by the fan 32. Becausethe coil surface 36 is warmer than the outdoor air it gives up heat tothe outdoors but still maintains proper pressure of the refrigerant inthe system 10 for 100% capacity operation.

Under varying capacity demands and varying outdoor temperatures theoutdoor unit 12 has a built-in control logic that opens and closescircuits within the condenser coil and also varies the speed of the fan32 to maintain a minimum pressure of the refrigerant in the system 10for stable operation. The lower the temperature outside, the fewercondenser circuits are active and the lower the speed of the fan 32. At,e.g., approximately 23° F. outdoor air temperature, the minimum amountof coil circuits are active and the speed of the fan 32 is at a minimum.As the outdoor air temperature continues to drop, the pressure of therefrigerant in the system also drops, which tends to cause the operationof the system to become unstable and the capacity of the system to startto drop off. Also, wind blowing against the back or side coil surfacescan make this negative impact even more dramatic since the coil surfacesare exposed.

In order to combat the negative impact of ambient air temperaturesdropping a below a low outside air threshold temperature of, e.g., 23°F. and wind on the operation of the system 10, the outdoor unit 12, asdepicted in FIG. 5, preferably includes a discharge hood 40 positionableover the fan 32 and attachable to the top 31 of the enclosure 30 aboutthe fan 32 to capture the fan discharge. In addition, the outdoor unit12 preferably includes wind deflectors 60 attachable to the sides 38 andthe back 34 of the enclosure 30 positioned over the coil openings 35.With a discharge hood 40 and wind deflectors 60 installed, the outdoorunit can maintain stable operation below the low outside air thresholdtemperature of 23° F., preferably down to about −13° F. and, morepreferably, down to about −10° F.

Turning to FIGS. 5 and 6, the discharge hood 40 preferably includes abox like enclosure 41 with a control box 50 mounted on the exterior ofthe enclosure 41. The enclosure 41 includes an opening 42 at its bottomwith mounting flanges 43 disposed about the periphery of the opening 42.The discharge hood 40 includes a discharge outlet 44 on one end or sideof the enclosure 41. The hood 40 further includes a damper assembly 45comprising a series of damper blades 46, 47 and 48 that are rotatablycoupled to the enclosure 41 in its interior adjacent the dischargeoutlet 44. The blades 46, 47 and 48 extend across the outlet 44 and canbe rotated to vary the opening of the discharge outlet 44.

Where the outdoor unit 12′ comprises two fans 32 and 32′, as depicted inFIG. 4B, a second hood 40′, as shown in FIG. 7, identical to the firsthood 40 with the exception of the control box 50, can be mounted to theenclosure 30 of the outdoor unit 12′. The first and second hoods 40 and40′ are preferably controllable by the control box 50 mounted on thefirst or master hood 40. The second hood 40′ being configured as a slavehood 40′ that is controllable by the master hood 40.

Turning to FIGS. 8 and 9, the wind deflectors 60 preferably include anopen box like body 61 having a face 64 and side 63 panels with mountingflanges 62 extending the length of the side panels 63. Top and bottomplates 65 and 66 extend at an angle from the top and bottom edges of theface panel 64 to a point approximately midway along the top and bottomedges of the side panels 63. When mounted on the enclosure 30 of theoutside unit 12, the wind deflectors 60 and the enclosure 30 form airflow openings 67 and 68 positioned at the top and bottom of the winddeflectors 60. In addition to the wind deflectors 60 preventing windfrom entering the coil face area within the enclosure 30 of the outdoorunit 12, the special angle of the top and bottom plates 65 and 66 of thewind deflectors 60 forms an air curtain preventing excessive air fromblowing up through the bottom opening 68 or down through the top opening67 of the wind deflectors 60. However, air can still be drawn in asneeded by the inverter driven condenser fan 32.

In one embodiment, a low ambient temperature kit can be provided forfield installation of a discharge hood and wind deflectors. The kitpreferably that includes one or more discharge hoods 40 and one or morewind deflectors 60. Preferably, the kit would include a sufficientnumber of discharge hoods 40 to cover all the fans 32 of the outdoorunit 12 and a sufficient number of wind deflectors 60 to cover all coilopenings in the enclosure 30 of the outdoor unit 12.

Turning to FIGS. 10, 11, 12 and 13, operation of the outdoor unit 12with a low ambient temperature kit installed is described. During normaloperation with the outdoor air temperature above the low outside airthreshold temperature, as depicted in FIG. 10, the fan 32 of the outdoorunit 12 draws air around the tops and bottoms of the wind deflectors 60and discharges air through the open damper 45 (i.e., the damper blades46, 47 and 48 are horizontally aligned at an angle of 0° to thehorizontal or top of the enclosure 31) and out the discharge outlet 44of the discharge hood 40. The air is drawn across the coil surface whichis under or behind the wind deflectors 60. The deflectors 60 are mountedon the back 34 and sides 38 of the unit 12. Because the coil surface iswarmer than the outdoor air it gives up heat to the outdoors but stillmaintains the proper pressure for efficient operation. Above the lowoutside air threshold temperature in cooling operation, air is notrestricted at all by the discharge hood 40. The condensing pressures aremaintained by opening and closing sections in the condenser coil andalso varying the speed of the fan 32. Above the low outdoor airthreshold temperature the operation is the same as if there were no lowambient kit installed.

During cooling operations below the low outside air thresholdtemperature, as depicted in FIG. 11, the outdoor unit 12 draws airaround the tops and bottoms of the wind deflectors 60 and discharges airthrough the damper 45 and out the discharge outlet 44 of the dischargehood 40. The air is drawn across the coil surface of the heat exchangerwhich is under or behind the wind deflectors 60. The coil surface iswarmer than the outdoor air so it gives up heat to the outdoors. Sincethe air is below the low outside air threshold temperature only a smallcondenser circuit is active and the condenser fan 32 is operating at itslowest speed. The condensing pressure continues to drop as the outdoortemperature continues to drop further below the low outside airthreshold temperature. To maintain a stable condensing pressure, thedamper assembly 45 partially closes to a position that is a function ofthe outdoor ambient temperature where the blades 46, 47 and 48 arepositioned at a predetermined angle to the horizontal. By partiallyclosing the damper assembly 45 and reducing or constricting the openingof the discharge outlet 44, airflow through the condenser coil of theoutdoor unit 12 is reduced even further than enabled by the minimumspeed of the fan 32. As the outdoor temperature continues to drop, thedamper assembly 45 continues to close further reducing the airflow. Ifthe load in the indoor space increases, more airflow across the coil isrequired to maintain a suitable condensing pressure. In this case thespeed of the fan 32 will increase to force more air through thepartially closed damper 45. For varying load conditions, the condensingpressure is tuned or adjusted by adjusting the speed of the fan 32

During heating operation, as depicted in FIG. 12, the outdoor unit 12coil is colder than the outdoor temperature. As air is drawn across thecoil, heat is absorbed from this air. The result is the air dischargedthrough the damper assembly 45 is colder than the incoming air. For aheat pump to operate efficiently in heating mode, the air through thecoil of the outdoor unit must be unobstructed. The damper control boxassembly 50 is interlocked with the outdoor unit reversing valve 70 (seeFIG. 14). When the unit 12 switches into heating mode (energizes thereversing valve 70) a relay 55 in the damper control box 50 isenergized. This relay 55 breaks power to the damper actuator controlcircuit 50, deenergizing the actuator motor 52. The motor 52 has aspring return feature that drives it to the full open position. Thisinterlocking relay function assures that the damper 45 will be wide openduring the heating mode allowing full airflow and full capacity.

When the unit 12 is operating in heating mode, frost and/or ice willbuild up on the fin surfaces 36′of the heat exchanger and needs to beoccasionally removed by means of a defrost cycle. As depicted in FIG.13, this is accomplished by shutting off the outside fan 32 entirely andswitching the reversing valve 70. By switching the reversing valve 70,the unit is now in essence running in the cooling mode. The coil is nowbeing heated from the energy left in the indoor units and piping.

The control box 50 views this as a cooling mode and the damper 45 willpartially close down to a position equal to what it would be in coolingmode for the outside ambient air temperature. For example, if it was 5°F. outside and the unit was operating in cooling, the damper may beclosed 50%. Now if the unit is in defrost mode the control box 50 reactsas if it were in cooling and the damper 45 is closed to 50%. The actionof the damper 45 closing during defrost and the wind deflectors 60protecting the coil from wind will increase defrost efficiency and thusshorten the length of defrost cycle. Shorter defrost cycles will yieldan overall increased heat output.

Turning to FIG. 14, the control box 50 includes a weather tightenclosure 51, a damper actuator 52 mounted to a control board 57 withinthe enclosure 51, a circuit board 53 coupled to the damper actuator 52,a control transformer 54 coupled to the circuit board 53, an interlockrelay 55 coupled to the control transformer 54, and a thermistor 56coupled to the circuit board 53 and extending through the enclosure 51to the outside. The damper actuator 52 preferably comprises a motor thatturns a shaft of the damper assembly 45 based on a control input. Theturning of the damper shaft causes the damper 45 to either open orclose. The input that causes the motor to move is preferably a controlvoltage signal within a control voltage signal range having upper andlower threshold voltages such as, e.g., a control voltage range of 2-10volt DC. Between the lower and upper threshold voltages, e.g., 2 and 10volts, is the control range. At the lower threshold voltage, the motorstarts to move. At the upper threshold voltage, the motor has reachedits full stroke or range of movement. The actuator 52 preferrably has arange of motion between 0° and 90° . Preferably, at a 0° angle, thedamper 45 is fully open. At a 90° angle the damper 45 preferably wouldbe fully closed. In a preferred embodiment, however, the damper 45 doesnot totally close. The furthest the motor will be allowed to turn theshaft of the damper 45 would be to angle position less than 90° such as,e.g., an 85° angle position, which leaves the damper 45 partially opensuch as, e.g., approximately 5-6% open. This limit is programmed intothe circuit board 53.

The relay 55 has a normally closed contact. Any time the outdoor unit 12is in cooling mode power is allowed to flow through the contact,allowing the damper 45 to operate by closing down as the outdoortemperature drops and opening up as the outdoor temperature rises. Thecolder it gets, the further the damper 45 closes.

The main purpose of the relay 55 is to allow the damper 45 to springreturn to a full open position when and if the unit 12 operates in aheating mode. The reversing valve 70 will be energized when the unit 12goes into heating mode. The relay 55 is tied into the control board 57at the connection for the reversing valve 70. This energizes the coil ofthe relay 55, opening the contact. When the contact opens power isdisconnected from the transformer 54, which de-energizes the controlboard 57 and power to the damper actuator 52. The damper 45 then springreturns to full open position to allow full airflow through the outdoorunit 12 for full heating capacity.

When the unit 12 is operating in heating and a demand for defrost isrequired the reversing valve 70 deenergizes. This de-energizes the relay55. The damper 45 is now allowed to operate in cooling mode, i.e., go toa partially closed position based on the outdoor temperature.

The resistance of the thermistor 56 changes based on the outsidetemperature. The thermistor 56 protrudes through the bottom of thecontrol box 50 so that it can sense the outdoor ambient temperature. Thecircuit board 53 receives a resistance value of the thermistor 56corresponding to the outside temperature.

The circuit board 53 is designed to take the resistance value from thethermistor 56 and convert it to a control voltage within a controlvoltage range such as, e.g., 2-10 volt DC output voltage, to control theposition of the damper actuator 52. In response to the control voltagereceived, the damper actuator 52 rotates the damper 45 to apredetermined angle corresponding to the input voltage. At or below thelower threshold voltage, e.g., 2 volts DC, which corresponds to outsidetemperatures at or above an upper threshold control temperature such as,e.g., 23° F., the actuator motor will retain the damper in the fullyopen position (i.e., at a 0° angle to the horizontal). As the DC voltageincreases in accordance with a drop in outside temperature, the damperactuator 52 will rotate the damper 45 toward a closed position. Since itis preferred not to fully close the damper 45 (at a damper angle of 90°,the damper is 100% closed), the closed position of the damper 45 ispreferably limited to a damper angle less than 90° such as, e.g., anangel of 85° , which corresponds to a control voltage signal input limitof less than 10 volts DC such as, e.g., 9.56 volts DC. Thus, at or abovethe upper threshold voltage, e.g., 9.56 volts DC, which corresponds tooutside temperatures at or below a lower threshold control temperaturesuch as, e.g., 3° F., the actuator motor will retain the damper 45 inthe closed position.

The programming of the circuit board 53 also has a built in hysteresisor differential so that the damper 45 does not move back and forthcontinuously based on very slight temperature fluctuations. Instead thecircuit board 53 is programmed to cause the damper actuator 52 tooperate or move in steps. As the outside temperature cools below athreshold temperature, the actuator 52 does not move the damper 45toward a partially closed angle until the temperature reaches a closepoint temperature. As the outside air temperature continues to cool, theactuator 52 does not move the damper 45 toward a further partiallyclosed angle until the temperature reaches the next close pointtemperature. For example, as the outside air temperature drops below 21°F., the damper 45 remains at an angle of 10° from horizontal until theair temperature drops to 18° F. wherein the damper 45 closes more byrotating to an angle opening of 25° from horizontal. Similarly, as theoutdoor temperature begins to warm, the actuator 52 does not move thedamper 45 toward a less partially closed angel until the temperaturereaches an open point temperature. For example, as the air temperaturewarms from 3° F., the damper 45 remains at an angle of 70° fromhorizontal until the air temperature reaches 7° F. wherein the damper 45rotates to an angle opening of 55° from horizontal. This allows stableoperation of the damper assembly 45 without a continuous hunting backand forth motion.

Turning to FIGS. 15A and 15B, in an alternative embodiment an outdoorunit 12 includes a discharge hood 140 with an integral wind deflector141. The discharge hood 140 includes a discharge outlet 144 and a damperassembly 145 comprising a series of damper blades 146, 147 and 148 thatare rotatably coupled to the discharge hood 140 in its interior adjacentthe discharge outlet 144. The blades 146, 147 and 148 extend across theoutlet 144 and can be rotated to vary the opening of the dischargeoutlet 144. The discharge hood 140 and integral wind deflector 141 caninclude a second damper assembly 150 comprising a series of damperblades 151 and 152 that are rotatably coupled to the wind deflector 141in its interior adjacent the level of the fan 32 and an opening of thewind deflector 141 into the discharge hood 140. As discussed below, whenthe outside temperature is low, the damper blades 146, 147 and 148adjacent the discharge outlet 144 can be moved to a closed position andthe damper blades 151 and 152 in the wind deflector can be moved to anopen position so that most of the discharged air from the fan will beturned back to the coil surface 36 without going out from the hood 140.In this configuration, the outside unit 12 performs heat exchange withthe discharged air from the outside unit 12 which is warmer than theoutside air. This enables the condensing temperature to be higher andthe workload of the compressor to be lighter.

During normal operation with the outdoor air temperature above the lowoutside air threshold temperature, as depicted in FIG. 15A, the fan 32of the outdoor unit 12 draws air around the tops and bottoms of the winddeflectors 60 on the sides of the unit 12 and around the bottom of thewind deflector 141 of the discharge hood 140 on the back of the unit 12,and discharges air through the open damper 145 (i.e., the damper blades146, 147 and 148 are horizontally aligned at an angle of 0° to thehorizontal or top of the enclosure 31) and out the discharge outlet 144of the discharge hood 140. The air is drawn across the coil surfacewhich is under or behind the wind deflectors 60 and 141. As shown,damper assembly 150 is closed (i.e., the damper blades 151 and 152 arehorizontally aligned at an angle of 0° to the horizontal or top of theenclosure 31) to insure the air is drawn across the coil surface whichis under or behind the wind deflector 141 of the discharge hood. Becausethe coil surface is warmer than the outdoor air it gives up heat to theoutdoors but still maintains the proper pressure for efficientoperation. Above the low outside air threshold temperature in coolingoperation, air is not restricted at all by the discharge hood 140. Thecondensing pressures are maintained by opening and closing sections inthe condenser coil and also varying the speed of the fan 32. Above thelow outside air threshold temperature the operation is the same as ifthere were no low ambient kit installed.

During cooling operations below the low outside threshold temperature,as depicted in FIG. 15B, the outdoor unit 12 draws air around the topsand bottoms of the wind deflectors 60 on the side of the unit 12 andaround the bottom of the wind deflector 141 of the discharge hood 140 onthe back of the unit 12 and discharges air through the damper 145 andout the discharge outlet 144 of the discharge hood 140. The air is drawnacross the coil surface of the heat exchanger which is under or behindthe wind deflectors 60 and 141. The coil surface is warmer than theoutdoor air so it gives up heat to the outdoors. Since the air is belowthe low outside air threshold temperature only a small condenser circuitis active and the condenser fan 32 is operating at its lowest speed. Thecondensing pressure continues to drop as the outdoor air temperaturecontinues to drop further below the low outside air thresholdtemperature. To maintain a stable condensing pressure, the damperassembly 145 partially closes to a position that is a function of theoutdoor ambient air temperature where the blades 146, 147 and 148 arepositioned at a predetermined angle to the horizontal and the damperassembly 150 opens where the blades 151 and 152 are positioned at apredetermined angle to the horizontal.

Turning to FIGS. 16A and 16B, in another alternative embodiment anoutdoor unit 12 includes a discharge hood 140 with an integral winddeflector 141. The discharge hood 140 includes a discharge outlet 144and a damper assembly 145 comprising a series of damper blades 146, 147and 148 that are rotatably coupled to the discharge hood 140 in itsinterior adjacent the discharge outlet 144. The blades 146, 147 and 148extend across the outlet 144 and can be rotated to vary the opening ofthe discharge outlet 144. A second damper assembly 150 comprising aseries of damper blades 151 and 152 that are rotatably coupled to thewind deflector 141 in its interior adjacent the level of the fan 32. Athird damper assembly 155 comprising a series of damper blades 156 and157 that are rotatably coupled to the wind deflector 141 in its interioradjacent an opening at the bottom of the wind deflector 141. Asdiscussed below, when the outside temperature is low, the damper blades146, 147 and 148 adjacent the discharge outlet 144 and damper blades 156and 157 adjacent the opening of the wind deflector 141 can be moved to aclosed position and the damper blades 151 and 152 in the wind deflectorcan be moved to an open position so that most of the discharged air fromthe fan will be turned back to the coil surface 36 without going outfrom the hood 140. In this configuration, the outside unit 12 performsheat exchange with the discharged air from the outside unit 12which iswarmer than the outside air. This enables the condensing temperature tobe higher and the workload of the compressor to be lighter.

During normal operation with the outdoor air temperature above the lowoutside air threshold temperature, as depicted in FIG. 16A, the fan 32of the outdoor unit 12 draws air around the tops and bottoms of the winddeflectors 60 on the sides of the unit 12 and around the bottom of thewind deflector 141 of the discharge hood 140 on the back of the unit 12,and discharges air through the open damper 145 (i.e., the damper blades146, 147 and 148 are horizontally aligned at an angle of 0° to thehorizontal or top of the enclosure 31) and out the discharge outlet 144of the discharge hood 140. The air is drawn across the coil surfacewhich is under or behind the wind deflectors 60 and 141. As shown, thedamper assembly 150 is closed (i.e., the damper blades 151 and 152 arehorizontally aligned at an angle of 0° to the horizontal or top of theenclosure 31) and the damper assembly 155 is open (i.e., the damperblades 156 and 157 are oriented at an angle to insure maximum air flow)to insure the air is drawn across the surface which is under or behindthe wind deflector 141 of the discharge hood 140. Because the coilsurface is warmer than the outdoor air it gives up heat to the outdoorsbut still maintains the proper pressure for efficient operation. Abovethe low outside air threshold temperature in cooling operation, air isnot restricted at all by the discharge hood 140. The condensingpressures are maintained by opening and closing sections in thecondenser coil and also varying the speed of the fan 32. Above the lowoutside air threshold temperature the operation is the same as if therewere no low ambient kit installed.

During cooling operations below the low outside air thresholdtemperature, as depicted in FIG. 16B, the outdoor unit 12 draws airaround the tops and bottoms of the wind deflectors 60 on the sides ofthe unit 12 and around the bottom of the wind deflector 141 of thedischarge hood 140 on the back of the unit 12 and discharges air throughthe damper 145 and out the discharge outlet 144 of the discharge hood140. The air is drawn across the coil surface of the heat exchangerwhich is under or behind the wind deflectors 60 and 141. The coilsurface is warmer than the outdoor air so it gives up heat to theoutdoors. Since the air is below the low outside air thresholdtemperature only a small condenser circuit is active and the condenserfan 32 is operating at its lowest speed. The condensing pressurecontinues to drop as the outdoor temperature continues to drop furtherbelow the low outside air threshold temperature. To maintain a stablecondensing pressure, the damper assembly 145 partially closes to aposition that is a function of the outdoor ambient air temperature wherethe blades 146, 147 and 148 are positioned at a predetermined angle tothe horizontal, the damper assembly 150 opens where the blades 151 and152 are positioned at a predetermined angle to the horizontal, and thedamper assembly 155 closes where the blades 151 and 152 are positionedat a predetermined angle.

Alternatively, a damper assembly could be positioned at the base of thefan 32 eliminating the discharge hood.

Turning to FIG. 17, as an alternative to the thermister 56 used tomeasure the outside temperature, the control system 50 could include oneof a variety of other sensors. For example, the control system 50 couldinclude an evaporating temperature sensor 160 located after the expander24, a low pressure sensor 162 located on the low pressure side of thecompressor, a condensing temperature sensor 164 located after thecompressor 28, or a high pressure sensor 166 located on the highpressure side of the compressor 28.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

1-26. (canceled)
 27. A method of defrosting the condenser coil of anoutdoor heat pump unit coupled to one or more indoor units comprisingthe steps of turning off the condenser fan, and reversing the flow ofrefrigerant from the indoor units through the condenser coil from arefrigerant flow direction corresponding to a heating operation to arefrigerant flow direction corresponding to a cooling operation.
 28. Themethod of claim 27, wherein the step of reversing the flow ofrefrigerant includes deenergizing a reversing valve.
 29. The method ofclaim 28, wherein the outdoor heat pump further comprises a dischargehood with a damper mounted on the interior adjacent a dischargeropening, further comprising the step of deenerging a relay couple to adamper motor.
 30. The method of claim 29, further comprising the step ofclosing the damper as a function of outside ambient air temperature. 31.The method of claim 30, wherein the outdoor heat pump unit includes aplurality of wind guards.
 32. The method of claim 31, wherein one of theplurality of wind guards is integarally formed with the discharge hood.